what kind of water to use may depend on what is in your tap water. it is my understanding that most photo chemicals today contain an ingredient to combat some hard water contaminants. if you think it is pretty free of rust, or other impurities, tap water is the way to go.
if you think it is not, you may want to consider distilled, or purified, drinking water. as stated, though, good tap water is the preferred way.
jim